The invention is in the field of railway wheels and, more particularly, relates to preventing shattered-rim fracture in railway wheels.
Recently, railroad transport volume, which is sometimes expressed in terms of railroad freight revenue ton-miles, has been increasing to meet an increasing rail transport demand. As a result, railway cars are hauling ever-heavier average loads. For instance, lightweight aluminum coal cars, which can have maximum gross loads up to 286,000 lbs., have become increasingly common. The wheel loads in such xe2x80x9cheavy haulxe2x80x9d coal cars are approaching permissible limits, a circumstance which results in lower load safety margins for the wheels of such rail cars.
One serious problem with railway wheels is known as shattered-rim fracture.
Shattered-rim fracture is a phenomenon whereby a rolling contact fatigue crack initiates at an internal defect in the wheel rim subsurface and propagates to ultimately cause substantial damage to the wheel. Left unchecked, the shattered-rim fracture can cause catastrophic failure of the railway wheel and derailment of the rail car. This problem can be exacerbated with increasing wheel speed, unbalanced loads, heavy braking, and other circumstances common in the railway industry.
Given the general increase in freight revenue ton-miles in the rail industry, there is an increasing need to prevent shattered-rim fracture in railway wheels.
It is a general object of the invention to provide a method for preventing catastrophic failure of railway wheels.
Another object of the invention is to provide a method for more effectively preventing shattered-rim fracture in railway wheels.
A further object is to provide a method for testing railway wheels for load suitability during intended usage.
Still another object is to provide a method for grading railway wheels as to load suitability.
Yet another object is to provide methods as characterized above that can be easily and effectively carried out.
Another object is to provide methods of the foregoing types that can be selectively carried out at different safety level rankings.
It is believed that a major cause of the shattered-rim fracture phenomenon is Mode II (in-plane shearing) crack propagation from defects in the rim of the railway wheel. It has now been discovered that shattered-rim fracture in railway wheels can be substantially avoided if the rim of the wheel does not contain defects of a size such as to lead to a Mode II stress intensity factor range (xcex94KII) at the maximum intended load that is greater than the threshold Mode II stress intensity factor range (xcex94KIITH) required for cracks to propagate from the defect. The invention makes use of this discovery to prevent shattered-rim fracture in railway wheels. In general, the invention contemplates an analysis of the likelihood of Mode II crack propagation from defects in the rim of a railway wheel. Such analysis may be used to determine the suitability of a railway wheel for carrying a maximum intended load, or alternatively, may be used to determine the maximum suitable load for a railway wheel.
In accordance with a highly preferred embodiment of the invention, a method is provided for more efficiently and effectively preventing shattered-rim fracture in a railway wheel. Generally, the method comprises providing a railway wheel that is expected to be subjected to an intended load, measuring the size of the largest defect within the rim of the wheel, and determining whether the defect size of this defect is below a pre-determined maximum permissible defect size for the intended load. The predetermined maximum defect size is ascertained by evaluating the likelihood of crack propagation from the defect upon subjecting the wheel to the intended load. In accordance with another highly preferred embodiment of the invention, the method for preventing shattered-rim fracture generally comprises the steps of measuring the maximum size of defects in the railway wheel rim, and determining the maximum usage load suitable for said wheel based on a predetermined correspondence between permissible load and defect sizes.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: